In regards to protection of intellectual property rights, there are various software copyright problems. Examples of the problems include illegal use and distribution of software products and copyright infringement caused by program plagiarism in software production. Among the problems, the use of illegal software can be easily detected. However, regarding the program plagiarism problem, it is difficult to determine whether plagiarism is made or not.
To address such problems, several methods of detecting program plagiarism have been studied. In the conventional methods which have been proposed so far to measure a program similarity, source codes of programs are analyzed and numericalized in various manners so as to determine a similarity between two programs to be compared with each other. Specifically, comparison is performed by using software metrics, or by comparing a token array of source codes or comparing function call relationships, or by analyzing a tree structure. In particular, researches on a method of detecting plagiarized programs from students assignments are widely being conducted, and a variety of results are being released by many universities worldwide. In this regards, systems (e.g., Plague, YAP3, MOSS, Clonechecker, etc.) have been introduced, in which source programs are input so that plagiarism is detected by measuring a similarity between two source programs. Disadvantageously, however, these conventional methods can be used only when source programs are obtained.